An image projection apparatus is used in a state where the image projection apparatus is connected to an image transmission apparatus, for example, a personal computer, in order to project content for presentation onto a projection surface, for example. A known image transmission apparatus generates display image data using a display image of a display device as a unit and displays an image on the display device using the generated display image data. Accordingly, in the case of displaying an image displayed on the display device by using the image projection apparatus, it was not possible to meet such a request that some content on a display screen, for example, only content for presentation of a presenter be displayed, since the display image data was transmitted to the image projection apparatus.
In order to solve such a problem, a technique of outputting window data of a window, which is selected from a plurality of windows displayed on a display device by a mouse pointer, to an external monitor as referred to in Japanese Patent Publication No. JP-A-2000-339130.
However, in the case where a plurality of image projection apparatuses were connected to an image transmission apparatus, it was not possible to transmit a plurality of contents displayed on a display device to the desired respective image projection apparatuses. In addition, in the case of content some of which was displayed on a display device, it was not possible to project the entire content through the image projection apparatus.
In addition, this problem is not limited to an image transmission apparatus to which a plurality of image projection apparatuses are connected but is a common problem in an image transmission apparatus to which a plurality of external display devices are connected.